Method and apparatus for network management using periodic measurements of indicators

ABSTRACT

A beacon signal used in data communications, such as the IEEE 802.11, is provided with data extensions. The data extensions permit additional information to be provided by the beacon signal, thereby reducing the traffic overhead of the network. The data extensions further permit handoffs and handoffs based on offset values. Periodic beacon requests are made during connection between a wireless transmit/receive unit (WTRU) and an access point (AP) on a WLAN. A Measurement Request field corresponding to a beacon request contains a measurement duration value and channel number for which the request applies. The beacon request permits a scan mode which includes “Active Scan” mode, “Passive Scan” mode and “Beacon Table” mode. In Active Scan mode, the measuring station (STA) transmits a probe request with a broadcast SSID. In Passive Scan mode, the measuring STA passively receives on the specified channel and return a beacon report containing one information element for each STA from which it detects a beacon or probe response. In Beacon Table mode, the measuring STA returns a beacon report containing the current contents of its beacon table without performing additional measurements.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. provisional application No.60/470,256 filed on May 14, 2003, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

This invention relates to beacon measurement request signals used inwireless slotted communications and network management. Moreparticularly, the invention relates to network management using periodicmeasurements of parameters such as new beacon received power level orsignal quality.

BACKGROUND

The IEEE 802.11 communications protocol allows a client to roam amongmultiple access points that may be operating on the same or separatechannels. IEEE 802.11 communications are generally effected throughwireless LAN access points (APs), which are typically single standaloneunits, but can include networks with multiple APs which provide aroaming function. To support the roaming function, each access pointtypically transmits a beacon signal every 100 ms. A roaming station(STA) uses the beacon to gauge the strength of its existing access pointconnection. If the STA senses a weak signal, the roaming STA canimplement the reassociation service to connect to an access pointemitting a stronger signal.

IEEE 802.11 supports two power modes; active and power-saving (PS). Theprotocols for infrastructure networks and ad hoc networks are different.Under an infrastructure network, there is an AP to monitor the mode ofeach mobile station. A station in the active mode is fully powered andthus may transmit and receive at any time. On the contrary, a station inthe PS mode only wakes up periodically to check for possible incomingpackets from the AP. A station always notifies its AP when changingmodes. Periodically, the AP transmits beacon frames spaced by a fixedbeacon interval. A PS station should monitor these frames. In eachbeacon frame, a traffic indication map (TIM) are delivered, whichcontains IDs of those PS stations with buffered unicast packets in theAP. A PS station, on hearing its ID, should stay awake for the remainingbeacon interval. Under the contention period (i.e., DCF), an awake PSstation can issue a PS-POLL to the AP to retrieve the buffered packets.While under the contention-free period (i.e., PCF), a PS station waitsfor the AP to poll it. The AP sends delivery TIMs (DTIMs) within beaconframes to indicate that there are buffered broadcast packets. Thedelivery TIMs are spaced by a fixed number of beacon intervals.Immediately after DTIMs, the buffered broadcast packets are sent.

Since IEEE 802.11 presumes that mobile stations are fully connected, thetransmission of a beacon frame can be used to synchronize all stations'beacon intervals. In addition to the use in IEEE 802.11, beacon signalsare useful in other WLAN communications and wireless communications ingeneral. Periodic measurements are performed in systems implementing thethird generation partnership program (3GPP) wideband code divisionmultiple access (W-CDMA) system. Such systems use a time division duplexmode. To support higher layer functions in IEEE 802.11 standards forefficient network management, several physical parameters relating todifferent aspects of network management are desirable.

One such parameter is the perceived signal to noise indicator (PSNI),the measurement of which provides a quantized, comparative measure ofreceived signal quality for all channels/rates and among all physicalchannels and between all stations. Another parameter is the receivedchannel power indicator (RCPI) indicator, which is a measure of thereceived RF power in the selected channel, measured at the antennaconnector. The RCPI parameter may be a measure by the PHY sub layer ofthe received RF power in the channel measured over the PLCP preamble andover the entire received frame. RCPI is a monotonically increasing,logarithmic function of the received power level defined in dBm. Theexemplary allowed values for the RCPI parameter may be an 8-bit value inthe range from 0 through 220.

In known approaches, the measurement of the parameters RCPI and PSNI isdone as a single measurement, which approach has certain disadvantages.It is desirable to provide an improved method of making measurements ofthe parameters, e.g., RCPI and PSNI, to result in specific advantagesresulting in more efficient network management.

SUMMARY

According to the present invention, periodic measurements of the newbeacon request are used in order to support roaming and dynamic datarate adjustment, and related functions. The concepts for periodicmeasurements are performed in a manner analogous to periodicmeasurements in systems implementing third generation partnershipprogram (3GPP) wideband code division multiple access (W-CDMA) systemutilizing the time division duplex mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a network configuration in which WLANscommunicate with a wireless transmit/receive unit (WTRU) through one ormore access points.

FIG. 2 is a chart showing types of measurements or reports.

FIG. 3 is a graph showing the effects of absolute threshold on data rateselection.

FIG. 4 is a graph showing a relative threshold which uses the serving APfor a handoff.

FIG. 5 is a graph showing the effect of a reporting offset.

FIG. 6 is a graph showing the received channel power indicator (RCPI)level of a serving AP.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment, mobile station, fixed or mobile subscriberunit, pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, an access pointincludes but is not limited to a Node B, site controller, access pointor any other type of interfacing device in a wireless environment.

An “access point” (AP) in a typical IEEE 802.11 implementation is astation or device which provides wireless access for devices toestablish a wireless connection with a LAN, and establishes a part of awireless LAN (WLAN). If the AP is a fixed device on a WLAN, the AP is astation which transmits and receives data. The AP permits connection ofa WTRU to a network, provided that the WLAN itself has a connection tothe network.

Network management by making measurements of parameters, e.g., RCPI andPSNI, is performed periodically rather than in the manner of a one-timemeasurement. The impact of making periodic measurements on the networkperformance and the attendant benefits are addressed in the descriptionof the preferred embodiment. More specifically, the beneficial effect ofmaking periodic measurements on the beacon request extensions to supportroaming and dynamic data rate are addressed. Even though the inventionis described in the specific context of the standard IEEE 802.11 as anexample, the invention is envisaged to be applicable to other scenariosalso.

Periodic beacon requests are made during connection between a WTRU andan AP on a WLAN. A Measurement Request field corresponding to a beaconrequest contains a measurement duration value and channel number forwhich the request applies. The beacon request permits a scan mode whichincludes “Active Scan” mode, “Passive Scan” mode and “Beacon Table”mode. In Active Scan mode, the measuring station (STA) transmits a proberequest with a broadcast service station identifier (SSID). Themeasuring STA's beacon report contains one information element for eachSTA from which it detects a beacon or probe response, regardless ofwhether the probe response was triggered by the measuring STA's ownprobe request. In Passive Scan mode, the measuring STA passivelyreceives on the specified channel and returns a beacon report containingone information element for each STA from which it detects a beacon orprobe response. If the measuring channel is also the serving channel,the STA concurrently carries out its normal data traffic operation. InBeacon Table mode, the measuring STA returns a Beacon Report containingthe current contents of its beacon table without performing additionalmeasurements. The Measurement Duration field is set equal to theduration of the requested measurement, expressed in time units (TUs).

The following are some potential advantages of periodic measurements ascompared with the single measurement approach:

Periodic measurements reduce management traffic: single measurementrequest produces multiple reports but only when relevant.

Absolute Threshold crossings on PSNI measures are ideal to trigger datarate changes.

Absolute Threshold crossings on RCPI are ideal for proximity detectorsfor location.

Relative Threshold with respect to serving AP detects conditions forhandoff.

The beacon request also contains periodic extensions (informationfields) which specify periodic beacon measurements. The extensionsfields are used to provide parameters for the periodic measurement andconditional reporting of measurement results. These provide periodicmeasurements which reduce management traffic, such that a singlemeasurement request produces multiple reports. The multiple reports areprovided only when deemed relevant. Absolute threshold crossings onperceived signal to noise indicator (PSNI) may be used as a condition toprovide a measurement report. The measurements on PSNI are suitable totrigger data rate changes. Absolute threshold crossings on receivedchannel power indicator (RCPI) may be used as a condition to provide ameasurement report.

The periodic extensions are additional fields in the beacon requestwhich are use for periodic beacon measurements. The capability to doperiodic measurements is an optional capability for the AP, andtherefore APs which are not capable of doing periodic beaconmeasurements will ignore the periodic extensions. A beacon request is arequest to perform a measurement. A beacon report is the responsecontaining the result(s) of the requested beacon measurement.

The absolute threshold crossings are suitable for proximity detectorsused to determine location and approximate position relative to an AP. Arelative threshold with respect to a serving AP is used to detectconditions for a handoff.

The measurement request field corresponding to a beacon request is shownin Table 1 and contains the measurement duration and channel number forwhich the request applies. Also included in Table 1 are the extensions(additional information fields) needed to specify periodic measurementsand conditional reporting. Table 1 generally shows the measurementrequest field format for a beacon request. The illustration for thecurrent measurement shows the number of octets for the channel number,channel band, measurement duration and scan mode. Table 1 also shows forcomparison, the octets for periodic extensions, with respect to basicservice set identifier (BSSID), measurement period, reporting condition,threshold/offset, and hysteresis effect. More particularly, theMeasurement Request field corresponding to a beacon request is shown inTable 1 and contains the measurement duration and channel number forwhich the request applies. A response to a beacon request is a beaconreport. TABLE 1 Beacon Request Channel Channel Measurement Scan NumberBand Duration Mode Octets: 1 1 2 1 Measurement Reporting Threshold/BSSID Period Condition Offset Hysteresis Octets 6 2 1 1 1

If the AP is not capable of performing periodic measurements and thusdoes not recognize the extensions, then the AP ignores the extensionsand provides a single measurement and a single report.

In Table 1, channel number indicates the channel number on which therequesting STA instructs the receiving STA to report detected beaconsand probe responses. In the beacon request, the Channel Number fieldindicates the channel number on which the requesting STA instructs thereceiving STA to report detected beacons and probe responses. TheChannel Band field indicates the frequency band, taken from Table 1, inwhich the receiving STA conducts its measurement. The Scan Mode field isset to the type of scan, according to Table 2 (infra). The scanningbehavior is as follows:

-   -   In Active Scan mode, the measuring STA transmits a probe request        with the broadcast SSID. The measuring STA's beacon report        contains one information element for each STA from which it        detects a beacon or probe response, regardless of whether the        probe response was triggered by the measuring STA's own probe        request    -   In Passive Scan mode, the measuring STA passively receives on        the specified channel and return a beacon report containing one        information element for each STA from which it detects a beacon        or probe response. If the measuring channel is also the serving        channel, the STA concurrently carries out its normal data        traffic operation.    -   In Beacon Table mode, the measuring STA returns a beacon report        containing the current contents of its beacon table without        performing additional measurements.

The Measurement Duration field is set equal to the duration of therequested measurement, expressed in TUs.

Tables 2 and 3 show channel band definitions for radio measurementrequests and Scan Mode definitions for beacon request elements. TABLE 2Channel Band definitions for radio measurement requests Name ChannelBand 2.4-GHz Band 0   5-GHz Band 1

TABLE 3 Scan Mode definitions for Beacon Request elements Name Scan ModePassive Scan 0 Active Scan 1 Beacon Table 2 Reserved 3-255

BSSID indicates the BSSID of the particular AP for which thismeasurement is requested. The BSSID specifies which AP to measure whenseveral APs are detectable on a given channel. The BSSID is set to thebroadcast BSSID when the measurement is performed on any AP(s) on thischannel. A broadcast BSSID is used when an AP BSSID is unknown.

The Measurement Period indicates whether this measurement is a singlemeasurement event or is a periodic measurement which is repeated eachMeasurement Period. The Measurement Period is divided into twosubfields: Unit and Period. The Unit subfield defines the time unit forthe Period subfield and consists of the 2 MSBs with the followingvalues:

The Period subfield consists of the 14 LSBs and is an unsigned integernumber representing the repeating time interval for this periodicmeasurement. A Period subfield value of 0 indicates that the measurementis not periodic but is a single measurement. A period subfield value of16383 (3FFF Hex) indicates that the measurement is periodic with norequested measurement period; in this case the measurement is performedon a best effort basis and as frequently as conditions permit.

The Reporting Condition defines when the measured results are reportedto the requesting STA. The Reporting Condition values are defined inTable 4. TABLE 4 Reporting Condition Definitions for Beacon RequestElement Reporting Condition Description Condition Report to be issuedafter each measurement. 0 Report to be issued when the RCPI level of themeasured AP 1 crosses above an absolute threshold with hysteresis.Report to be issued when the RCPI level of the measured AP 2 crossesbelow an absolute threshold with hysteresis. Report to be issued whenthe PSNI level of the measured AP 3 crosses above an absolute thresholdwith hysteresis. Report to be issued when the PSNI level of the measuredAP 4 crosses below an absolute threshold with hysteresis. Report to beissued when the RCPI level of the measured AP 5 crosses above athreshold defined by an offset (with hysteresis) from the serving AP'sRCPI. Report to be issued when the RCPI level of the measured AP 6crosses below a threshold defined by an offset (with hysteresis) fromthe serving AP's RCPI. Report to be issued when the PSNI level of themeasured AP 7 crosses above a threshold defined by an offset (withhysteresis) from the serving AP's PSNI. Report to be issued when thePSNI level of the measured AP 8 crosses below a threshold defined by anoffset (with hysteresis) from the serving AP's PSNI. Periodic reports(one per measurement) to begin when the 9 RCPI level of the measured APenters and remains in a range bound by the serving AP's RCPI and anoffset (with hysteresis) from the serving AP's RCPI. Periodic reports(one per measurement) to begin when the 10 PSNI level of the measured APenters and remains in a range bound by the serving AP's PSNI and anoffset (with hysteresis) from the serving AP's PSNI. Reserved 11-255

Threshold/Offset provides either the threshold value or the offset valueto be used for conditional reporting. A threshold value is an unsigned 8bit integer having units which are equivalent to PSNI or RCPI. An offsetvalue is a signed 7 bit integer in the range of (−127, +127).

Hysteresis provides an unsigned 8 bit integer hysteresis value havingunits equivalent to the units used in the Threshold/Offset field.

FIG. 1 is a schematic diagram of a network configuration 11 in which oneor more WLANs 12, 13 communicate with a WTRU 15 through one or more APs17-19. In the example depicted the WLANs 12, 13 are able to establish anetwork link 22, either directly or through a radio network controller(RNC) 23.

FIG. 2 is a chart showing types of measurements or reports, showing howevent detection triggers a report, or, triggers periodic reporting. Morespecifically, FIG. 2 illustrates for comparison, a single reportscenario for PSNI and RCPI, as compared to similar periodic conditionalreports for absolute threshold, serving AP threshold, serving APperiodic range. Also illustrated is the periodic reporting for eachtrigger event for comparison. The broadest category is a measurement 26.As used here, “measurement” can be a measurement or report. Themeasurement 26 may be a single 27 or periodic 28 measurement. A singlemeasurement generates a single report 29, which includes a single reportPSNI 30 and a single report RCPI 31. The periodic measurement 28 cangenerate a conditional report 32 or a periodic report 33. Theconditional report 32 can provide an absolute threshold 34, a serving APthreshold 35 or a serving AP periodic range 36. The absolute threshold34 includes an absolute threshold PSNI 37 and an absolute threshold RCPI38. The serving AP threshold 35 includes a serving AP threshold PSNI 47and a serving AP threshold RCPI 48. The serving AP periodic range 36includes a serving AP periodic range PSNI 57 and a serving AP periodicrange RCPI 58. The periodic report 33 includes a periodic report PSNI 67and a periodic report RCPI 68.

In addition, the single report 31 may be conditionally reported based onan absolute threshold 34 including absolute threshold PSNI 37 andabsolute threshold RCPI 38. Also, the single report 31 may beconditionally reported based on the serving AP threshold 35 includingserving AP threshold PSNI 47 and serving AP threshold RCPI 48. Theserving AP periodic range is not used for the single report 31, but mayprovide the serving AP periodic range 36 including serving AP periodicrange PSNI 57 and serving AP periodic range RCPI 58 for periodicmeasurement reporting.

The single and periodic measurements 27, 28 are measurement types. Thesingle report 31, conditional report 32, periodic report The absolutethreshold 34, serving AP threshold 35 and serving AP periodic range 36trigger events. The measurement results are the single report PSNI 27,single report RCPI 28, absolute threshold PSNI 37, absolute thresholdRCPI 38, serving AP threshold PSNI 47, serving AP threshold RCPI 48,serving AP periodic range PSNI 57, serving AP periodic range RCPI 58,periodic report PSNI 67 and periodic report RCPI 68. For conditionalreporting, event detection triggers one or more of these single eventreporting outputs or periodical reporting outputs.

FIG. 3 is a graph showing the effects of absolute threshold on data rateselection, and illustrates variation of measurement quantity againsttime for three different channels having 5.5 Mbps, 2.0 Mbps and 1.0 Mbpsrates respectively. At an initial time of the graph, STA 1 receives alow PSNI level from the AP as measured at the STA, substantially belowan absolute threshold. The rate is established at 1 Mbps. STA 2 and STA3 have PSNI levels above the threshold level. As time progresses, STA 3has received PSNI levels which exceed a second threshold and then dropsdown to below the absolute threshold. STA 3 thus can change to the 5.5Mbps rate, but must drop down to the 2 Mbps rate and eventually the 1Mbps rate as the PSNI level drops. STA 2 remains at the 2 Mbps rateuntil later, when STA 2 has sufficient PSNI levels to change to the 5.5Mbps rate. These changes in PSNI levels can also be used to change APsby selecting the AP with a higher rate or PSNI level, should resourcesfrom that AP be available.

FIG. 4 is a graph showing a relative threshold which uses the serving APfor a handoff. This figure also illustrates variation of measurementquantity against time for AP 1 and AP 2 intersecting at a locationshowing the reporting event. The graph shows the signals received by aSTA from a first AP (Serving AP) and a second AP (AP 2). The measurementfor the servicing AP is made lower by an offset, in which PSNI is madelower, in order to favor AP 2. Thus the measurement of PSNI for theserving AP is made artificially lower by the offset. This causes anearly trigger of the handoff as a result of the offset.

FIG. 5 is a graph showing the effect of a reporting offset and showsrelative threshold triggers for AP 1, 2 and 3 showing the reportingrange and when the reporting terminates. The graph illustrates timeslotISCP versus time showing the ISCP threshold and the reporting event.Event triggered and periodic reports of the PSNI levels each show theinstance of a reduced PSNI level as a result of the offset. Thereporting of the serving AP 3 continues during a peak period of PSNIreported from a third AP, AP 3, but discontinues when the signal from AP3 drops below the offset reporting of PSNI from the serving AP.

FIG. 6 is a graph showing the RCPI level of a serving AP. The triggeringevent here is an absolute threshold exceeded. The triggering eventtriggers a report.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone (without the other features andelements of the preferred embodiments) or in various combinations withor without other features and elements of the present invention.

1. In a wireless communication system utilizing at least one accesspoint transmitting a beacon signal responsive to a beacon request, thebeacon signal used for indicating channel, measurement and mode data, amethod for extending the system to incorporate additional signalinformation, the method comprising: providing at least one extension ofthe beacon request, the extension providing a measurement of a signalcondition.
 2. The wireless communication system of claim 1, wherein theextension including one of BSSID, measurement period, reportingcondition, threshold, offset of measurement and hysteresis.
 3. Thewireless communication system of claim 1, wherein the extensionincluding one of PSNI and RCPI measurements.
 4. The wirelesscommunication system of claim 1, wherein the wireless communicationsystem implementing a wireless LAN connection and the beacon signalprovided in the implementation of the LAN connection.
 5. The wirelesscommunication system of claim 1, wherein: a response protocol includes abeacon extension; and the beacon extension includes a Period subfieldprovided as an unsigned integer number representing a repeating timeinterval for a periodic measurement.
 6. The wireless communicationsystem of claim 1, wherein: a response protocol includes a beaconextension; and the beacon extension including a Period subfield, thePeriod subfield comprising 14 LSBs as an unsigned integer numberrepresenting a repeating time interval for a periodic measurement,wherein a Period subfield value of 0 indicates a single non-periodicmeasurement.
 7. The wireless communication system of claim 1, whereinthe beacon request extension includes a Period subfield provided as anunsigned integer number representing a repeating time interval for aperiodic measurement.
 8. The wireless communication system of claim 1,wherein the beacon request extension including a Period subfield, thePeriod subfield comprising 14 LSBs as an unsigned integer numberrepresenting a repeating time interval for a periodic measurement,wherein a Period subfield value of 0 indicates a single non-periodicmeasurement.
 9. In a wireless local area network (WLAN), a method foroperating an access point (AP) utilizing a beacon signal, the methodcomprising: providing, in the beacon signal, periodic measurements inresponse to beacon requests in order to support one of roaming, dynamicdata rate adjustment, and related signal control functions.
 10. Themethod of claim 9, wherein the WLAN implementing a WLAN connection andthe beacon signal provided in the implementation of the WLAN connection.11. The method of claim 9, wherein the extension includes one of BSSID,measurement period, reporting condition, threshold, offset ofmeasurement and hysteresis.
 12. The method of claim 9, wherein extensionincluding one of PSNI and RCPI measurements.
 13. The method of claim 9,wherein: a response protocol including a beacon extension; the beaconextension includes a Period subfield provided as an unsigned integernumber representing a repeating time interval for a periodicmeasurement.
 14. The method of claim 9, wherein: a response protocolincluding a beacon extension; and the beacon extension including aPeriod subfield, the Period subfield comprising 14 LSBs as an unsignedinteger number representing a repeating time interval for a periodicmeasurement, wherein a Period subfield value of 0 indicates a singlenon-periodic measurement.
 15. The method of claim 9, wherein the beaconrequest extension includes a Period subfield provided as an unsignedinteger number representing a repeating time interval for a periodicmeasurement.
 16. The method of claim 9, further characterized by abeacon request extension including a Period subfield, the Periodsubfield comprising 14 LSBs as an unsigned integer number representing arepeating time interval for a periodic measurement, wherein a Periodsubfield value of 0 indicates a single non-periodic measurement.
 17. Ina wireless local area network (WLAN) including at least one access point(AP) and at least one wireless transmit/receive unit (WTRU), a methodfor operating a WTRU, the method comprising: providing a beacon requestincluding at least one measurement response; receiving a beacon signalin response to the request; and if provided in the beacon signalobtaining the measurement response.
 18. The method of claim 17, whereinthe measurement response includes one of a measurement to supportroaming, a measurement to support dynamic data rate adjustment, and ameasurement to support a related signal control function.
 19. The methodof claim 17, wherein the wireless communication system implementing aWLAN connection and the beacon signal provided in the implementation ofthe WLAN connection.
 20. The method of claim 17, wherein a beaconrequest extension includes one of BSSID, measurement period, reportingcondition, threshold, offset of measurement and hysteresis.
 21. Themethod of claim 17, wherein a beacon request extension includes one ofPSNI and RCPI measurements.
 22. The method of claim 17, wherein: aresponse protocol including a beacon extension; and the beacon extensionincluding a Period subfield provided as an unsigned integer numberrepresenting a repeating time interval for a periodic measurement. 23.The method of claim 17, wherein: a response protocol including a beaconextension; and the beacon extension including a Period subfield, thePeriod subfield comprising 14 LSBs as an unsigned integer numberrepresenting a repeating time interval for a periodic measurement,wherein a Period subfield value of 0 indicates a single non-periodicmeasurement.
 24. The method of claim 17, wherein a beacon requestextension including a Period subfield provided as an unsigned integernumber representing a repeating time interval for a periodicmeasurement.
 25. The method of claim 17, a beacon request extensionincluding a Period subfield, the Period subfield comprising 14 LSBs asan unsigned integer number representing a repeating time interval for aperiodic measurement, wherein a Period subfield value of 0 indicates asingle non-periodic measurement.